I bought a new 2017 Ford Ranger double-cab. I found grey silicone sealant and the numbers 10, 20 and 5 hand-painted on the rear differential. Does this mean work was done on the differential, or is this how it is released from the factory?
They are indicators that show work was done on the differential, but they're not anything should be on concern. Cars have all sorts of marks on them from production, they usually indicate a check has been done along the way.